Mass base modifications

ESI and MALDI-MS are routinely used for both accurate mass information on intact proteins and their proteolytic digests. As a result these methods have already helped detect viral mutants, identify capsid proteins, and post-transla-tional modifications. Recent work has also included the detection of the first intact viral particles as well as a viral protein capsid. Other mass-based approaches like time-resolved proteolysis is giving new insight into the dynamics of viral capsid proteins in solution. This information, when combined with complementary information from X-ray crystallography studies is leading to a better understanding of viral structure and function. 

Tandem mass spectrometry coupled to electrospray ion source allowed not only to identify proteins but also to characterize post-translational modifications of a protein (phosphorylation, acetylation, methylation, glycosylation, etc.). Indeed, the presence of such modifications induces an increase of the peptide molecular masses compared to the calculated masses based on the theoretical sequence, which often directly identifies the type of modification. In addition, tandem mass spectrometry allows in general precise localization of the modification at specific residue of the peptide. Analysis of modifications allows to understand biological mechanisms because several processes are controlled and/or induced by such modifications (Mann and Jensen 2003). Being... 

These new algorithms made it possible to calculate the derivative couplings for general polyatomic molecules with much improved efficiency and accuracy. As discussed in Chapter 2 of this volume, the ACj j(X) produces a mass dependent modification to a Born ppenheimer potential energy surface that can be inferred from measurements of ro-vibronic energy levels of the isotopomers. Indeed, using the Bj j(X) determined at the MRCI level, we were able to resolve a discrepancy in the adiabatic correction for LiH(X E ) obtained from an analysis of experimental data, and from a theoretical prediction, based on highly specialized wave functions, see Sec. 8. 

Laser based mass spectrometric methods, such as laser ionization (LIMS) and laser ablation in combination with inductively coupled plasma mass spectrometry (LA-ICP-MS) are powerful analytical techniques for survey analysis of solid substances. To realize the analytical performances methods for the direct trace analysis of synthetic and natural crystals modification of a traditional analytical technique was necessary and suitable standard reference materials (SRM) were required. Recent developments allowed extending the range of analytical applications of LIMS and LA-ICP-MS will be presented and discussed. For example ... 

The results of this analysis are shown in Figure 5.16, which contains the UV trace, at 220 nm, and the equivalent mass spectral trace. In this case, the mass spectral data are represented by a modification of a reconstructed ion chromatogram (RIC) known as the base-peak trace, i.e. a plot of the intensity of the base peak in each scan (the m jz value of this may well vary from scan to scan) as a function of time. 

The experiments were carried out with two initiators. According to published data (B.), at the base temperature, Tb, the fast initiator, II, has a half-life of 3.5 minutes, and the slow initiator, 12, has a half-life of 95 minutes. A minor modification of the monomer mass balance (Equation 7) is required for the case of two initiators. 

Krahmer, M. T. Johnson, Y. A. Walters, J. J. Fox, K. F. Fox, A. Nagpal, M. Electrospray quadrupole mass spectrometry analysis of model oligonucleotides and polymerase chain reaction products determination of base substitutions, nucleotide additions/deletions, and chemical modifications. Anal. Chem. 1999, 71, 2893-2900. 

Confirmation of the modification of the hydroxyl end groups from the PPG can be accomplished by analysis using MALDI-TOF MS [59]. An example MALDI-TOF mass spectrum of a prepolymer based on PPG 2000 is shown in Figure 28. End group and average molecular weight data can be gleaned from the spectrum. The dominant distribution of peaks centred at approximately m/z 2,500... 

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